DESCRIPTION (Abstract of the Core) Core D will provide technical support for experiments requiring measurement of the interactions of gut peptides and other peptide growth factors with cell surface receptors and the subsequent intracellular signaling events that result from those interactions. Originally, this core functioned primarily to provide support for investigators to measure the binding of various radiolabeled peptide ligands to cell surface receptors, and this remains a major resource of Core D. During the previous two funding periods, this core expanded its scope to include measurements characterizing several of the important intracellular signal transduction pathways which result from such ligand-receptor interactions. Therefore, in addition to labeling any of the peptides under study add evaluating their binding to cellular membrane receptors, Core D now routinely performs determinations of intracellular Ca 2+ concentrations (( Ca 2+)i), adenylate cyclase activity, cyclic AMP or cGMP levels, phosphatidylinositol hydrolysis, protein kinase C (PKC) and mitogen-activated protein kinases (MAP kinases). During the last funding period, the heaviest use of the core was for measurement of ( Ca 2+)i. However, in the project period, additional demands by the projects and investigators in the program led to approximately 60 procedures for cAMP and radioiodinations sufficient to support 75 ligand binding assays. During the last funding period, 21% of the 186 publications produced by the group have utilized the facilities and expertise provided in Core D.